1. Field of the Invention.
The present invention relates to remediation methods that depend on the injection or extraction of fluids to or from porous media.
2. Description of the Art.
Subsurface soil and groundwater in an aquifer may be contaminated by a variety of organic or inorganic chemical compounds. Various remedial methods have been used to reduce or destroy these contaminants in place. Four of those remedial methods were: 1) Soil Vapor Extraction; 2) Aquifer Sparging; 3) Biodegradation; and 4) Direct Oxidation (that is, oxidant injection). Each of these four remedial methods depends on the injection or extraction of fluids to or from porous media.
Generally, in these prior systems, one or more injection wells have been constructed on the site to be remediated. Each injection well has had one injection point, usually consisting of a slotted well screen placed below the base of the contaminant plume in the soil. For sparging and soil vapor extraction, one or more extraction wells have been constructed on the site. Such prior systems have generally been effective in injecting desired liquid or gaseous fluids into contaminated areas in soils that comprise homogeneous, coarse-grained geologic formations.
However, as reported by Steven P. Sittler and Michael A. Hansen in "Innovative Air Sparging Techniques," Industrial Wastewater, July/August 1997 at page 20, experts estimate that fewer than 25% of remediation sites nationwide are conducive to conventional air sparging because many sites have varying geologic and hydrogeologic conditions. For example, the site could have a one or more lenses of low permeability material such as silt or clay within the phreatic zone; there could also be other geologic formations of low-conductivity. With the vertical sparge or injection point below the lens, the sparge air bubbles could travel around the lens, missing any contaminant above the lens, for example, and leaving potentially significant pockets of dissolved contaminant in the groundwater. Similar problems would be expected with the other remedial methods that depend on the injection or extraction of fluids to or from porous media, wherein the non-homogeneous porous media may block the path of a pocket of vapor to be extracted, or the path of the biodegradation material or oxidant to all of the affected areas of soil.
Various techniques have been attempted to solve the problems presented by non-homogeneous site conditions. Extensive and expensive sampling of the soil has been performed in an attempt to fully and accurately define the geologic formations. Once the geologic formations have been defined, multiple wells have been installed in different bore holes at what was interpreted to be the proper elevations. With separate well bores at separate depths, fluids could then be transferred at different levels. The expense of this technique has limited its utility. For sparging, another prior technique involved flow-through trench sparging in low permeability geologic formations. The need for horizontal trenching and the potential to generate large quantities of contaminated soil, however, has reduced the economic benefits of this technique.